Aromatics, particularly benzene, toluene, ethylbenzene, and the xylenes (ortho, meta, and para isomers), which are commonly referred to as “BTEX” or more simply “BTX,” are extremely useful chemicals in the petrochemical industry. They represent the building blocks for materials such as polystyrene, styrene-butadiene rubber, polyethylene terephthalate, polyester, phthalic anhydride, solvents, polyurethane, benzoic acid, and numerous other components. Conventionally, BTX is obtained for the petrochemical industry by separation and processing of fossil-fuel petroleum fractions, for example, in catalytic reforming or cracking refinery process units, followed by BTX recovery units.
Typically, integrated refining-petrochemical complexes separate a crude feedstock into a “straight run” or desired fraction of naphtha, such as C6-C10 naphtha, i.e., naphtha containing hydrocarbons having carbon chain lengths of six to ten, and a heavier fraction containing longer chain hydrocarbons such as heavy oils and residues. The naphtha stream typically undergoes reforming to produce a reformate with an increased aromatic content. The reformate is processed in an aromatics complex to produce selected aromatic products, such as benzene and para-xylene.
The heavier fraction is typically cracked, for example in a fluid catalytic cracking (FCC) unit, to form a “heart cut” or desired fraction of hydrocarbons, such as C6-C10 FCC hydrocarbons. FCC naphtha has had limited application in aromatic manufacture because of its alternate use in gasoline blending. In addition, olefins present in FCC naphtha may be converted into other less desired compounds if it combined with straight run naphtha and sent to a reformer. Furthermore, the presence of contaminants, such as sulfur, nitrogen, and dienes, affect aromatics extraction and reduce the hydrogen yield from reforming. As a result, virgin naphthas are typically used for aromatics.
Because aromatics are the building blocks of so many materials, there is a need to increase production of desired aromatics from integrated refining-petrochemical complexes. There is also a need to increase aromatics production without decreasing the value of other streams produced in the integrated refining-petroleum complexes, such as gasoline blends.
Therefore, there is a need for processes for converting FCC into aromatics.